About the accessibility issue in the Paris metro: this can be mitigated by using the buses (that's not the best experience but it works fine), and in some parts of Paris (in my experience, east and suburbs) people usually quickly help you in the stairs with your stroller (it's not convenient or comfortable to rely on others but in practice it seems to work). Anyway this is not like Paris mayor has any power on that, the transport authority though announced a few years ago that the main priority after the Grand Paris Express will be making the historical Paris network accessible. And fortunately after two years hopefully your kid can walk and you can carry it without a stroller.

> Local parks and generally streets are so dirty that you have to wash your children from head to toe as soon as they have set foot outside.

Maybe if it is a newborn, and if you don't bring the stroller nor any clothes, on rainy days it can be that bad. Don't get me wrong, Paris is not a clean city, there are empty nitrogen tanks, puffs and cigarettes lying on the ground pretty much in every arrondissement, but syringes, even on the colline du crack I can hardly remember having seen even one (but it is very dirty there! with packaging, paper, cardboard, bottles).

I still think there should be a higher priority on sanitation but I also think you are exaggerating a bit.